| Purpose:(1)The effect of different valgus angles on stress distribution and stability of tibia after open?wedge high tibial osteotomy was studied by finite element analysis.(2)The effect of tibial slope on the stress distribution and stability after high tibial osteotomy was studied under the same valgus angle.Methods:(1)A case of knee arthritis associated with medial compartment was selected and the scans of both low extremities were performed by computed tomography(CT).Then,the CT data was imported into three-dimensional model reconstruction software Mimics 17.0 for 3D reconstruction.In the three-dimensional model,the mechanical axis of lower extremity passed from 50%,55%,60%,65% and 70% of the tibial plateau width when measured from the edge of the medial tibia respectively according to the principle of high tibial osteotomy to determine the location and orientation of the osteotomy.Subsequently,we conducted the smoothing procedure in the Geomagic Studio and imported the data into SolidWorks software to build the model.The appropriate size of cancellous bone was implanted into the wedge-shaped opening of each model,and the finite element model was assembled with TomoFix plate.The assembled model was imported into Hypermesh software for meshing and assignment of material properties.Finally,the finite element processing software Aabaqus was used to constrain the boundary conditions.The compressive loads of 1000 N,1500N and 2000 N and the torsional loads of 20 NM were applied respectively.The stress distribution,stress peak and displacement of the high tibial osteotomy model under different valgus angles were compared.(2)The mechanical axis of lower leg was maintained in 55% of the medial-lateral width of the knee joint away from the medial edge after HTO.Next,in the sagittal plane the tibial posterior slope was changed to 4°,7°,10° and 13° respectively according to the first part of procedure.At the same time,1000 N,1500N and 2000 N of the axial load and 20 NM of the torsional load were applied to different tibial slope to compare stress distribution.Results:(1)Under axial load,there was no significant difference in stress distribution between different valgus angles and the cortical hinge was the site of stress concentration in the proximal tibia.In addition,the maximum value of the von Mises for the tibia was at 50% of the tibial plateau while the minimum was at 55%.For the Tomofix plate,the highly stressed volume which occurred at the front edge and the last screw was less than 100 MPa.Moreover,the stress-concentrated region did not change along with the alteration of valgus angles.With the increase of load,the stress of tibia and plate gradually increased as well as the displacement,and the difference between groups was not significant.The characteristics of the stress of the graft bone were consistent with the tibia which there was no obvious change with the alteration of valgus angle.The tip of cancellous bone was stress-concentrated region.(2)Under the axial load,the tibial slope had no significant effect on the stress distribution of the tibia and the plate,and the stress still concentrated on the hinge of the lateral tibia and the anterior edge of the plate.However,it can be found from the stress cloud of the bone that the stress-concentrated area moved from posterior medial to posterior lateral.When the tibial slope was at 10°,the maximum stress suffered by the tibia was significantly less than the other three groups.Under the torsional load,there is no obvious change of stress cloud,and there is no significant difference in the displacement of tibia between groups.Conclusions:(1)After the medial opening wedge osteotomy,the stress-concentrated region of the tibia was located at the lateral hinge.When the mechanical axis passed through 55% of the tibial plateau,biomechanical properties were more stable than other groups.(2)At the same valgus angle,the minimum stress was observed in 10° of tibial slope and it was important to maintain the inclination of tibial plateau. |
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